1. Field of the Invention
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device having a visual field angle while being capable of restraining or relaxing a gray scale inversion.
2. Description of the Related Art
Generally, the liquid crystal display device applies voltage to the liquid crystal in predetermined molecule arrays to change the liquid crystal in the other arrays, of which the liquid crystal cells undergoes a change of optical characteristics such as a double refractivity, a rotatory polarization, a dichroism and a light scattering according to the molecule arrays of the liquid crystal to emit the light. Therefore, the liquid crystal display device can display the images according to the changes of the optical characteristics of the liquid crystal cell.
The liquid crystal display device is typically divided into a twisted nematic type of the liquid crystal display device and a super twisted nematic type of the liquid crystal display device. According to an operation way, further, the liquid crystal display device is divided into an active matrix display way of the liquid crystal display device using switching elements and twisted nematic liquid crystal and a passive matrix display way of the liquid crystal display device using super twisted nematic liquid crystal.
There is a difference of the active matrix display type of the liquid crystal display device and the passive matrix display way of the liquid crystal display device in that the liquid crystal display device in the active matrix display way uses a thin film transistors as switches to operate liquid crystal while the liquid crystal display device in the passive matrix display way does not use transistors as it does not requires complex circuits. The liquid crystal display device using the thin film transistor is widely used as a lap top computer recently is popularized.
The liquid crystal display device comprises a liquid crystal display panel having liquid crystal to decide whether to transmit light as receiving electric signals. The liquid crystal display panel is a passive element that does not generates the light by itself. Accordingly, a backlight assembly is attached to a surface of the liquid crystal display panel in order to provide the light to the liquid crystal display device. Furthermore, the liquid crystal display panel has a source portion for applying image data to display images and a gate portion for applying gate signals to operate a gate element of the thin film transistor in the liquid crystal display panel, which are attached to the liquid crystal display panel. The liquid crystal in the liquid crystal display panel receives the electric signals when image signals are applied through the source portion and the gate portion to the transistor of the liquid crystal display panel. Thereby, the liquid crystal controls the light from the backlight assembly to make the images.
FIG. 1 is an exploded perspective view of showing a liquid crystal display device according to the conventional art and FIG. 2 is a sectional view of showing a liquid crystal display module of the liquid crystal display device in an-assembled state, shown in FIG. 1.
Referring to FIGS. 1 and 2, the liquid crystal display device 100 comprises a liquid crystal display module 200 for displaying images when image signals are applied thereto and front and rear cases 300 and 400 for receiving the liquid crystal display module.
The liquid crystal display module 200 includes a display unit 210 having a liquid crystal display panel for showing the images.
The display unit 210 includes a liquid crystal display panel 212, an integrated and printed circuit board 214, a tape carrier package 216 for date and a ductile printed circuit board 218 for gate. The liquid crystal display panel 212 includes a thin film transistor board 212a, a color filter board 212b and liquid crystal (not shown).
The thin film transistor board 212a is a transparent glass on which the thin film transistors are formed in matrix. Data lines are respectively connected with source terminals of the thin film transistors and gate lines connected with gate terminals of the thin film transistors. Furthermore, pixel electrodes are respectively formed at drain terminals of the thin film transistors, which are made of a transparent conductive material such as Indium Tin Oxide.
As being inputted to the data lines and the gate lines, the electric signals are applied to the source terminals and the gate terminals of each thin film transistor of the thin film transistor board 212a to turn on or turn off the thin film transistors according to an input of electricity, resulting in outputting the electric signals required to form pixels to the drain terminals.
The color filter board 212b is disposed to face to the thin film transistor board 212a in the display unit 210. RGB pixels are formed on the color film board 173 by means of a thin film process, which present a predetermined color while the light passes through the color film board 212b. Common electrodes made of Indium Tin Oxide are coated on the front surface of the color film board 212b.
The color filter board 212b has a compensatory film 213 and a polarizing plate 215 formed on an upper portion to improve a visual field angle.
When the thin film transistors of the thin film transistor board 212a are turned on by applying electricity to the gate terminals and the source terminals of the thin film transistors, electric field is created between the pixel electrodes of the thin film transistor board 212a and the common electrodes of the color filter board 212b. The electric field makes the liquid crystal, which is injected in a space between the thin film transistor board 212a and the color filter board 212b, to change the array angle thereof, resulting in that the permeability of the light is changed. As a result, it is possible to gain the desired pixels.
Meanwhile, a driving signal and a timing signal are applied to the gate lines and data lines of the thin film transistor in order to control the array angle of the liquid crystal and the time of arraying the liquid crystal in the liquid crystal display panel 212. As shown in FIG. 1, the data tape carrier package 216 is attached to the source portion of the liquid crystal display panel 212 to decide a time of applying a data driving signal. On the other hand, the gate tape carrier package 218 is attached to the gate portion of the liquid crystal display panel 212 to decide a time of applying a gate driving signal.
The integrated and printed circuit boards 214 which applies the driving signal to the gate line and the data line as soon as receiving image signals inputted from outside of the liquid crystal display panel 212, comes in contact with the data tape carrier package 216. The integrated and printed circuit board 214 receives the image signals provided from an information process device (not shown) such as a computer and the like and generates the gate driving signal and the data signal for operating the liquid crystal display device and a plurality of timing signals for applying the gate driving signal and the data signal to the gate lines and the data lines of the liquid crystal display panel 212.
The backlight assembly 220 is disposed under the display unit 210 to supply the light to the display unit 220 uniformly. The backlight assembly 220 includes a line typed lamp 222 which is disposed at an end of a liquid crystal display module 200, for generating the light.
A light guide plate 224 has a size corresponding to that of the liquid crystal display panel 212 of the display unit 210 and has a thickness which is gradually reduced from an end adjacent to the lamp 222 to the other end being far away from the lamp 222. The light guide plate 224 is disposed under the liquid crystal display panel 212 so as to guide the light generated by the lamp 222 to the display unit 210 while changing the pathway of the light.
A plurality of optical sheets 226 for making a brightness of the light, which is transmitted from the light guide plate 224, to be uniform is provided on the light guide plate 224. Further, a light reflecting plate 228 is provided under the light guide plate 224 to reflect a leaked light to the light guide plate 224 so as to improve the efficiency of the light.
The display unit 210 and the backlight assembly 220 are fixedly supported by means of a mold frame 230. The mold frame 230 has a rectangular tetragonal shape and an opening at a top portion thereof. That is, the mold frame 230 has four sidewalls and a bottom wall on which openings are formed so that the integrated and printed circuit board 214 is bent along an outer surface of the mold frame 230 to be received through the openings in the mold frame 230.
A chassis 240 is provided for the mold frame 230 in order to fix the integrated and printed circuit board 214 and the gate tape carrier package 218 of the display unit 210 to the bottom wall of the mold frame 230 while to bend the integrated and printed circuit board 214 and the gate tape carrier package 218 toward the outside of the mold frame 230.
The chassis 240 has a rectangular tetragonal shape similar to the mold frame 230, of which an upper surface is opened to expose the liquid crystal display panel 212 and sidewalls are inwardly bent to cover a peripheral surface of the liquid crystal display panel 212.
To assemble the liquid crystal display device, firstly, the backlight assembly 220 is received in the mold frame 230, on which in turn the display unit 210 is disposed. Next, the integrated and printed circuit board 214 connected through the data tape carrier package 216 to the display unit 210 is mounted in the openings formed in the bottom wall of the mold frame 230 while being bent along the outer surface of the sidewall of the mold frame 230. Finally, the chassis 240 is combined with the mold frame 230 so that the display unit 210 and the backlight assembly 220 are fixed to the mold frame 230.
At that time, the ductile circuit board 218 for gate, which is attached to the gate of the display unit 210, is fixed to the bottom wall of the mold frame 230 with enclosing the outer surfaces of the mold frame 230. An adhesive tape or a separate fixing member is used for fixing the ductile circuit board 218 for gate to the mold frame 230 in order to prevent the ductile circuit board 218 from departing from the mold frame 230.
The liquid crystal display device 100 according to the conventional art as described above has a compensative film 213 including a discotic layer in order to improve the visual field angle. In the case of using the compensative film 213, it is possible to improve the visual field angle relating to the contrast ratio. However, when the voltage is increased, it is difficult to improve a gray scale inversion in that the brightness of the light is rather reduced. Furthermore, in the case of a two domain twisted nematic mode, when the compensative film is used for improving the visual field angle, the compensated domain and the non-compensated domain are simultaneously presented in the liquid crystal display panel 212. Accordingly, there are problems in that even though it is possible to improve the visual field angle, it is impossible to improve the gray scale inversion and in that on the contrary when the gray scale inversion is improved, it is impossible to improve the visual field angle.